Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
  • B29C44/02—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles for articles of definite length, i.e. discrete articles
  • B29C44/04—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles for articles of definite length, i.e. discrete articles consisting of at least two parts of chemically or physically different materials, e.g. having different densities
  • B29C44/0415—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles for articles of definite length, i.e. discrete articles consisting of at least two parts of chemically or physically different materials, e.g. having different densities by regulating the pressure of the material during or after filling of the mould, e.g. by local venting
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
  • B29C44/02—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles for articles of definite length, i.e. discrete articles
  • B29C44/04—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles for articles of definite length, i.e. discrete articles consisting of at least two parts of chemically or physically different materials, e.g. having different densities
  • B29C44/0407—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles for articles of definite length, i.e. discrete articles consisting of at least two parts of chemically or physically different materials, e.g. having different densities by regulating the temperature of the mould or parts thereof, e.g. cold mould walls inhibiting foaming of an outer layer
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
  • B29C44/34—Auxiliary operations
  • B29C44/58—Moulds
  • B29C44/586—Moulds with a cavity increasing in size during foaming

Definitions

• the present invention relates to a method for injection molding a foamable plastic composition. More specifically, the molded plastic is a lightweight, highly heat-insulating, and more rigid foam plastic molded product that has a dense, non-foamed or low-foamed layer and a highly foamed layer inside.
• the present invention relates to an out-molding method.
• thermoplastic plastic composition containing a foaming agent is injected into a cavity having the same volume as a target molded article in an amount smaller than the volume of the cavity, and the composition is injected.
• a method is known in which the cavity is filled by utilizing the volume increase caused by foaming.
• it is difficult to completely fill the pedestal where the shape of the end portion of the target molded product is thin with the composition.
• the expansion ratio is 4 mm or more.
• the limit is 1.2 to 1.5 times, and at such a magnification, there remains a problem in the heat insulation properties and weight reduction of the obtained foamed plastic molded product.
• Japanese Patent Application Laid-Open No. 62-26710 discloses another method of manufacturing a foamed plastic molded article.
• a mold connected to an injection port of an injection molding machine is a fixed mold and the fixed mold is 3 ⁇ 4, j.
• the foaming agent is injected from the injection molding machine into the molding die, it is possible to enlarge and reduce the cavities formed in (ill) by moving the movable die back and forth.
• an injection molding method of a foamed resin in which a movable die is retracted to enlarge a cavity to a predetermined size.
• a mold that fits into each other and is relatively movable in the direction of expanding or reducing the volume of a cavity is positioned at a predetermined cavity volume reduction position.
• Foamable molten resin in the cavity The resin is compressed by moving the mold in the cavity one-volume expansion direction while injecting while maintaining the resin pressure at which the resin does not foam, and then compressing the resin by moving the mold in the cavity one-volume reduction direction.
• the solid is cooled and solidified, and then the mold is moved again in the direction of expanding the volume of the cavity to reduce the resin pressure at which foaming starts and foam the resin inside.
• a compression molding method is disclosed.
• the conventional method as described above has a problem that a molded article having an excellent appearance cannot be obtained.
• the volume of the cavity is enlarged at the same time as the injection, so that bubbles are ruptured on the surface of the molded product, and it is difficult to obtain a surface with no or low foaming and a dense cellular structure.
• complete filling may be difficult.
• a mold having a cavity structure having a thick portion at a position away from the gate for example, a mold for a molded product having a large flat portion and a shape having ribs, bosses, etc.).
• the shape of the molded product must be limited to a bar shape, a rectangular shape, or a shape that is sufficiently thick in the thickness direction with respect to the projected area of the plane portion. That is, it is intended to obtain a good molded product by a method including a step of expanding the cavity simultaneously with or during the injection. At times, it is not possible to escape the restriction that the shape of the molded product is limited to the gouging area.
• the present invention has been made in view of such problems of the prior art, and has been made by ordinary injection molding using a mold having a cavity structure having a thin portion at a position distant from the gate. It is a layer with a dense structure with no foaming or low foaming on the surface and a high foaming layer inside. It is intended to provide a shooting method.
• the present invention is a.
• the present invention relates to an injection molding method for a foamable plastic composition containing:
• the present invention also relates to a foamed plastic molded article manufactured by the above method.
• FIG. 1 is a perspective view showing the inside of a molded article manufactured in an embodiment according to the present invention
• FIG. 2 is a perspective view showing the bottom surface of the molded article manufactured in an embodiment according to the present invention.
• the gate position is indicated by 1
• the top surface and the site from which the test piece used for the test of rigidity and heat insulation is cut out are indicated by 2 c
• the foamable plastic composition used in the present invention contains a thermoplastic plastic and a foaming agent.
• the thermoplastic plastic include polypropylene, polyethylene, propylene-no-ethylene copolymer, polystyrene, polyvinyl chloride, polyvinylidene chloride, ABS resin, methacrylic resin, and polyvinyl alcohol.
• the foaming agent include inorganic compounds such as ammonium carbonate and sodium bicarbonate and organic compounds such as azo compounds, sulfohydrazide compounds, nitroso compounds and azide compounds.
• azo compound examples include azodicarbonamide (ADCA), 2,2'-azobisisobutyronitrile, azohexahydrobenzonitrile and diazoaminobenzene.
• ADCA azodicarbonamide
• nitroso compound examples include ⁇ , ⁇ ′-dinitrosopentamethylenetetramamine (D ⁇ ⁇ ⁇ ⁇ ) and ⁇ , ⁇ ′-dimethyl terephthalate.
• the azide compound examples include terephthalazide and tert-butylbenzazide.
• the foamable plastic composition used in the present invention can be prepared, for example, by distributing a foaming agent in an amount of 0.5 to 5% by weight with respect to a thermoplastic plastic and dry blending using a tumbler or the like.
• Cavity having a volume of 10 to 95% of the volume of the target molded product specified in the present invention is obtained by dividing the volume of the target molded product by the expansion ratio of the target molded product, for example. It can be expressed in volume. For example, if the size of the target molded product is 20 Ommx 20 Ommx 4 and the expansion ratio is 2, the cavity with 50% of the volume of the target molded product will be 200 x 200 mm x 2 Can be represented as ram.
• the expansion of the capacity of the cavity according to the present invention can be performed, for example, by moving the mold by a mold clamping mechanism of the mountain molding machine or by moving a slide core provided on the mold.
• Such a change in the volume of the cavity is desirably controlled by a force forming machine or a mold mechanism itself, which can also be performed by a manual operation.
• the pedestal that expands the capacity of the cavity by moving the mold due to the mold closing of the injection molding machine should have a control function that can move and stop the mold arbitrarily during the molding operation. If the capacity of the cavity is increased by moving the slide core, it is desirable to have a function that can control the movement of the slide core arbitrarily.
• the cooling according to the present invention until the solidified layer in contact with the mold surface and the internal molten layer coexist is performed, for example, by using a cooling mechanism of an injection mold, after the filling of the composition by injection is completed.
• the state of the cavity having a volume of 10 to 95% of the volume of the molded article to be prepared can be maintained for 1 to 20 seconds.
• the foamable plastic composition used in the present invention may contain, if necessary, an inorganic filler such as an antioxidant, a weathering agent, an ultraviolet absorber, an antistatic agent, a coloring agent, an olefin-based elastomer, and talc. It can be blended within a range that does not impair the purpose of the above.
• an inorganic filler such as an antioxidant, a weathering agent, an ultraviolet absorber, an antistatic agent, a coloring agent, an olefin-based elastomer, and talc. It can be blended within a range that does not impair the purpose of the above.
• the state of the cavity is in the contracted position while the foamable plastic composition is being injected into the cavity, that is, the cavity is contracted or enlarged during the injection to reduce the cavity.
• Change the volume The feature is that after injection is completed, cooling-expansion of cavities-re-cooling is performed. Therefore, the molded article obtained by this method is a layer having a dense structure with no foaming or low foaming on the surface and a highly foamed layer inside, and is excellent in appearance, heat insulation, and the like.
• the reason for obtaining a layer having a dense structure with no foaming or low foaming on the surface of the molded product is that the volume of cavity until the step b) above is the volume of the molded product
• the injection pressure and the holding pressure are transmitted to the end of the foamable plastic in the molten state in which the cavity is filled into the cavity, so that there is a thick portion at a position away from the gate.
• the foaming plastic in the molten state can be filled in the meat portion, and that complete filling is easy.
• the cooling step is performed until the solidified layer in contact with the mold surface and the internal molten layer are mixed, it is considered that the internal molten layer foams in the subsequent step c).
• step d) In order to cool and solidify inside in step d) above, the inside is highly foamed
• a molded article consisting of layers is obtained.
• Composition A 97 g by weight of a crystalline propylene homopolymer having a melt flow rate of 2.5 gZ for 10 minutes and a crystal melting point of 165 based on JISK 7210 test conditions 14 (230 ° C; 21.18 N) was used.
• Composition B Propylene homopolymer 85% by weight and propylene ethylene copolymer having an ethylene content of 60% by weight 15% by weight According to JISK7210 test conditions 14 (230 ° C; 21.18N) Based on melt flow rate of 2.5 minutes, 97 parts by weight of a crystalline propylene-ethylene block copolymer having a crystal melting point of 165 ° C, and 3 parts by weight of azodicarbonamide (ADCA). A composition obtained by stirring a mixing table in a tumbler-mixer.
• Composition C 9 g of crystalline propylene single base having a melt flow rate of 2.5 gZl 0 min and a crystal melting point of 165 based on JISK 7210 test conditions 14 (230 ° C; 21.18N) was used.
• ADCA azodicarbonamide
• Fig. 1 As shown in Fig. 1, it has a cavity for obtaining a box-shaped molded product with a length of 410 and a width of 295 mm. A height of 50 mm. A mold whose cavity volume can be changed at the mold position was used.
• Standard product A melt flow rate based on JISK 7210 test condition 1 (230 ° C; 21.18N) is 2.5 gZI O content of polypropylene.
• the cylinder set temperature was set at 210C and the cooling water temperature of the mold was set at 50C, and the thickness of the top surface was 5.
• Oram. Injection of 702 g into a cavity with a total volume of 78 Occ After the injection was completed, it was cooled for 50 seconds, and then the mold was opened and the molded product was taken out. This molded product was used as a standard product.
• a 100 ⁇ 100 test piece was cut out from the molded product obtained in each of the examples and comparative examples, and after measuring the specific gravity of each, the value was divided by the specific gravity of the standard product.
• the injection molding machine and the mold set the cylinder temperature of the injection molding machine to 230 ° C and the cooling water temperature of the mold to 70 ° C, and mold according to the following procedure. Was done.
• Example 3 Using the above composition A, an injection molding machine and a mold, the cylinder of the injection molding machine was set at a set temperature of 230, and a cooling water temperature of the mold was set at 70 ° C, and the following step (i) Except for this, molding was performed in the same procedure as in Example 1.
• the injection molding machine and the mold Using the above composition C, the injection molding machine and the mold, the cylinder of the injection molding machine was set at a set temperature of 230 ° C, and the cooling water temperature of the mold was set at 70 ° C. Molding was performed using the same procedure as in steps (i) to (iii). A molded article having a length of 410 ⁇ width of 29.5 mm ⁇ height of 52.8 mm (volume of 78 Occ) was obtained. Table 1 shows the properties of the obtained molded product.
• Injection was performed into a cavity having a top surface thickness of 5.0 mm and an overall volume of 78 Occ, and the injection of 39.6 g of the composition was completed in 3 seconds. After cooling for 120 seconds after the injection was completed, the mold was opened and the molded product was removed. A molded product with a length of 410 mm, a width of 295 and a height of 51.3 mm (capacity: 665 cc) was obtained. Table 1 shows the properties of the obtained molded product.
• the injection molding machine and the mold set the cylinder temperature of the injection molding machine to 230 ° C and the cooling water temperature of the mold to 70 ° C. Molding was carried out.
• volume expansion started 2 seconds after the start of shooting, and completed 1.5 seconds after the start so that the cavity thickness at the top was 5.0 and the total volume was 78 Occ. .
• the above composition ⁇ , the injection molding machine and the mold are supplied, and the cylinder of the injection molding machine is set at 230 ° C and the cooling water temperature of the mold is set at 7 () ° C. Molding was performed according to the procedure.
• the shooting mountain forming method according to the present invention can be performed by a normal injection molding machine using a mold having a cavity structure in which a blank portion is located at a position distant from the gate, so that it is economically excellent.
• the foamed plastic molded article manufactured by such a method has a layer having a dense structure with no foaming or low foaming on the surface and a highly foamed layer inside, and is lightweight, excellent in heat insulation, and more rigid. It is suitable for use in automobile parts, home appliances, general industrial ffl components, etc.

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• Injection Moulding Of Plastics Or The Like (AREA)

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• 1996
  • 1996-09-13 CN CN96180433.5A patent/CN1229382A/zh active Pending
  • 1996-09-13 EP EP96930404A patent/EP1013390A4/de not_active Withdrawn
  • 1996-09-13 WO PCT/JP1996/002639 patent/WO1998010912A1/ja not_active Application Discontinuation

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